The present invention relates to a method for producing a filter element suitable for a fuel filter, a lubricant filter and so forth.
For improving a filtering efficiency by increasing an effective filtering area in a limited volume of a filter, a honeycomb construction of sheet-shaped filter material without a chrysanthemum-flower-shaped bending construction of sheet-shaped filter material is proposed.
In disclosures of Japanese Patent Examined Publication No. 61-50612 and U.S. Patent Publication No. 2599604, a flat sheet filter material and a wave-shaped sheet filter material are fixed to each other to form a combination sheet with a plurality of first small holes therebetween and the combination sheet is rolled into a cylindrical body with the first small holes and a plurality of second small holes formed between adjacent layers in the rolled combination sheet. At an end of the cylindrical body, one end of each of the first small holes is filled with an adhesive to be hermetically sealed and ends of the second small holes are open. At another end of the cylindrical body, one end of each of the second small holes is filled with an adhesive to be hermetically sealed and ends of the first small holes are open, so that a liquid can flow through filtering areas formed between the second small holes and the first small holes. The combination sheet may consist of a pair of wave-shaped sheet filter materials fixedly connected to each other through adhered flat portions between semi-circular portions, as shown in FIG. 13.